Along-shelf Transport and Cross-shelf Exchange Driven by Surface Waves on the Inner Continental Shelf

内陆架表面波驱动的沿陆架运输和跨陆架交换

• 批准号: 1626466
• 负责人: Thomas Connolly
• 金额: $ 12.56万
• 依托单位: San Jose State University Foundation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-01 至 2019-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1626466&HistoricalAwards=false
• 关键词: Along; shelf; Transport; Cross; Exchange

Exchange across the inner shelf influences the distribution of nutrients, harmful algal blooms, pollutants, larvae and sediment. It is not yet fully understood how surface waves influence this exchange. Recent advances have been made in the numerical modeling of wave-current interactions, but so far these modeling studies have focused on the surf zone. This study will extend these modeling capabilities to the inner shelf by testing model results in the context of laboratory and field observations. This research will drive further development of wave-current coupling in a modeling system that is freely available to the scientific community. The insight into wave-current interaction processes gained during this investigation will improve the development of realistic models used in practical sediment transport applications. Most studies of inner-shelf circulation have focused on the role of wind stress. Surface waves have only recently been recognized as an important forcing mechanism over the inner shelf. Present understanding of the wave-driven inner-shelf circulation is based on analytical models with restrictive assumptions, such as constant turbulent mixing throughout the water column, and no spatial variations across the shelf. The model experiments in this study will allow for more realistic representations of turbulent mixing, and will include the effects of stratification, a sloping bottom and advection of momentum from the surf zone, where breaking waves generate strong along-shelf currents. Few previous studies have quantified the importance of momentum advection on the inner shelf, but it is potentially important near the boundary of the surf zone and will also be assessed in observations. Based on the model experiments, the relative importance of the hypothesized mechanisms under different environmental conditions will be scaled so that results can be applied generally at many locations. The goal of this study is to identify the key processes that determine the observed spatial structure of the circulation driven by surface waves on the inner shelf, which is located offshore of the breaking surf. Previous observations have identified a surface-intensified offshore flow associated with surface waves over the inner shelf. In the direction parallel to shore, new observational analysis shows a complex response to wave forcing that varies with water depth. Two alternative hypotheses are formulated to account for these observations: one in which the Earth's rotation is necessary, and another that involves strong turbulent mixing and transport of momentum from the surf zone. Numerical modeling experiments, with complex physics but idealized geometry, will be carried out to determine the relative contribution of these two mechanisms to the observed wave-driven circulation during different forcing and environmental conditions. A new parameterization for the critical process of "wave streaming" near the bottom will be tested against field and laboratory observations. Model experiments, in combination with new analysis of existing observations, will identify processes that generate exchange between the surf zone and inner shelf during combined wind and wave forcing.

跨内大陆架的交换影响营养物质、有害藻华、污染物、幼虫和沉积物的分布。目前还不完全了解面波是如何影响这种交换的。近年来，波流相互作用的数值模拟已经取得了一些进展，但到目前为止，这些模拟研究主要集中在海浪带。这项研究将通过在实验室和现场观察的背景下测试模型结果，将这些建模能力扩展到内陆架。这项研究将推动波流耦合在一个可供科学界免费使用的建模系统中的进一步发展。在本次研究中获得的对波流相互作用过程的洞察将促进实际泥沙输运应用中实际模型的发展。大多数关于陆架内环流的研究都集中在风应力的作用上。直到最近，表面波才被认为是内陆架上的一种重要的强迫机制。目前对波浪驱动的内陆架环流的理解是基于带有限制性假设的分析模型，例如整个水柱中的湍流混合是恒定的，并且整个陆架上没有空间变化。这项研究中的模型实验将允许更真实地表示湍流混合，并将包括分层、倾斜的底部和来自海浪带的动量平流的影响，在那里，破碎的海浪会产生沿陆架的强烈洋流。以前很少有研究量化内陆架上动量平流的重要性，但它在海浪带边界附近可能很重要，也将在观测中进行评估。在模型实验的基础上，将衡量假设的机制在不同环境条件下的相对重要性，以便结果可以在许多地点普遍应用。这项研究的目的是确定决定由表面波驱动的内陆架环流空间结构的关键过程，内陆架位于破裂海浪的近海。以前的观测已经确定了与内陆架上方的表面波有关的表面强化离岸流动。在与海岸平行的方向上，新的观测分析显示出对波浪强迫的复杂响应，这种响应随着水深的变化而变化。为了解释这些观测结果，提出了两种不同的假设：一种假设地球自转是必要的，另一种假设涉及强烈的湍流混合和来自海浪带的动量输送。为了确定这两种机制在不同强迫和环境条件下对观测到的波生环流的相对贡献，将进行具有复杂物理性质但具有理想化几何形状的数值模拟实验。根据现场和实验室的观测结果，将对接近底部的“波流”临界过程进行一种新的参数化检验。模型实验，结合对现有观测的新分析，将确定在风浪联合强迫期间在冲浪区和内陆架之间产生交换的过程。